New Zealand's food safety regulator will reconsider the safety of an artificial sweetener used in thousands of foods after a study linked it to leukemia in rats.

The Italian authors of the study, published in the European Journal of Clinical Oncology, have called for "urgent re-examination" of the safety of aspartame -- a commonly used sweetener 200 times sweeter than sugar but containing no calories.

The research showed many female rats fed aspartame developed lymphomas or leukemia at higher rates than the control rats -- the risk increasing with the dose of aspartame.

The study raised concerns about the levels of aspartame to which humans could be exposed.

Food Standards Australia and New Zealand spokesman Dean Stockwell said the agency would assess the study's significance and whether any action was needed.

The European food regulator also has promised an urgent evaluation of the research.

An industry source described the Italian paper as "unusual," as it went against all previous publications on the subject.

Concerns have been raised about aspartame in the past, but several research reviews, by regulators in Britain and the U.S., concluded it was not a health risk.